Electronic mail (e-mail) that is not requested is commonly referred to as ‘spam’, but is also known as “unsolicited commercial e-mail” (UCE), “unsolicited bulk e-mail” (UBE), “gray mail”, and the electronic equivalent of “junk mail”. The term spam can be used as both a noun (the e-mail message) and as a verb (to send it), respectively characterizing mail practically no one wants and the mailing of the same. Spam is used to advertise products and services, request charitable donations, or to broadcast some political or social commentary. Spamming is the practice of sending the same message by e-mail to large numbers of e-mail addresses indiscriminately. Spamming is considered bad manners in this digital world and unethical because it not only wastes everyone's time, but also costs money. The sender of the messages (the ‘spammer’) does not pay the cost. Rather, the cost is paid by the Web sites of the recipient and others on the route. Spam also eats up network bandwidth.
Like viruses, spam has become a scourge on the Internet as hundreds of millions of unwanted messages are transmitted daily to almost every e-mail recipient as well as to newsgroups. Unfortunately for users and fortunately for spammers, as an advertising medium, spam does produce results. Even if only an infinitesimal number of users reply, it is still cost effective since e-mail is a very inexpensive way to reach people.
There are many organizations, as well as individuals, who have taken it upon themselves to fight spam with a variety of techniques. In order to alleviate some spam, Internet Service Providers (ISPs) and other e-mail service providers have added servers that do spam filtering to divert incoming spam. Spam filters can be installed in the user's machine and/or in the mail server, in which case, the user never receives the spam. Spam filtering can be configured to trap messages based on a variety of criteria, including the sender's e-mail address, specific words in the subject or message body or by the type of attachment that accompanies the message. Address lists of habitual spammers (blacklists) are maintained by various organizations, ISPs and individuals as well as lists of acceptable addresses (whitelists) that might be misconstrued as spam. Spam filters reject blacklisted messages and accept whitelisted ones. Sophisticated spam filters use artificial intelligence techniques that look for key words and attempt to decipher their meaning in sentences in order to more effectively analyze the content and not reject for non-delivery a real message. Spam filters can also divert mail that comes addressed as “Undisclosed Recipients,” instead of having the e-mail address spelled out in the “to” or “cc” field.
Despite the user's best of efforts as well as those of the e-mail service provider that services the user, spam filtering is not always successful in that spam still finds its way to the user's e-mail address. In fact, because the Internet is public, no e-mail service provider can guarantee that its users will be prevented from receiving spam, just as it is nearly impossible for a governmental postal service to prevent the delivery of junk mail to addressees.
A significant and effective spamming technique known to spammers is a dictionary attack-based mass mailing of e-mails. To do this, the spammer creates or generates a list of different addresses that are derived from a dictionary of common words, phrases, and character sequences. As a result, the list will have many addresses that can be quite similar. For instance, the spammer may use such a dictionary to derive different combinations of user identifications (IDs). The user IDs, so derived, are consequently quite similar. The spammer, however, does not know in advance whether or not any of the addresses in the derived list are valid e-mail addresses. Nevertheless, the spammer sends the spam to the addresses corresponding to the different combinations of user IDs in the hope that a high percentage of the e-mail addresses will be valid e-mail addresses.
Dictionary attack-based mass mailing of e-mails exacts a high cost by wasting the time of the spam recipients and by sapping expensive resources away from e-mail service providers. It would be an advantage in the art to prevent the delivery of dictionary attack-based mass mailing of e-mails.